Generally, back lighting units, in which a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is used as a light source, have been used to provide light to a liquid crystal display (LCD) or the like. Among such back lighting units, a back lighting unit using a CCFL has disadvantages in that a great quantity of mercury is contained therein not to be environment-friendly and it is difficult to obtain the wavelengths for three uniform primary colors (blue, green and red) due to intrinsic characteristics of the CCFL to depreciate the color reproducibility.
On the contrary, a back lighting unit using a light emitting diode has advantages in that it is environment-friendly and it is easy to implement the wavelengths for three uniform primary colors to have excellent color reproducibility as compared with a CCFL. Furthermore, as high-intensity/high-powered light emitting diodes have been recently developed, the back lighting unit using the light emitting diode has been widely used for illumination of large-sized display devices such as medium to large scaled LCD devices.
Conventionally, methods for mixing primary color lights with each other have been used in the back lighting unit as described above in order to obtain white light for illuminating an object such as an LCD device. These methods are classified into one in which light emitting diode chips for emitting three primary color lights are used and the three primary color lights emitted from the chips are mixed to obtain white light and the other in which a light directly emitted from a light emitting diode chip and lights excited to have different colors by phosphors are mixed with each other. At this time, the phosphors in the latter method are generally contained in a molding member for enclosing the perimeter of the light emitting diode chip. However, the aforementioned back lighting unit has problems in that the space required for the color mixing is short, and both a diffusing sheet itself for diffusing the light and a precise design for the diffusing sheet are essentially required.